HEARING 409 



admitted as harmonies combinations which earlier generations 

 could not tolerate. 



Pitch, quality, harmony, and dissonance are distinguished 

 by the human ear. These are the attributes of musical or 

 periodic sounds. In a separate class must be included noises 

 of all kinds, termed in acoustics " aperiodic," because the 

 vibrations which cause them are not rhythmic. The teeth of 

 a policeman's rattle may click a hundred times a second, but 

 it does not make music. Even with a rapidity of interruption 

 greater than this (at least 500 times per second) a succession 

 of noises fails to blend into a smooth, continuous sound. The 

 ear recognizes the loudness, duration, and even to a very high 

 frequency the repetition of unmusical sounds. 



The ear as a sense-organ can be followed down the zoological 

 scale to jelly-fish. In its primitive form it is a chamber lined 

 with epithelial cells bearing hairs, containing an otolith, or 

 ear-stone. Otoliths are rounded calcareous masses which 

 play an important part in the ears of all animals up to fishes. 

 Even in man they are found in the more subdivided form of 

 otoconia. Contact of the otoliths with the sensory hairs 

 originates impulses in the nerves with which primitive ears 

 are abundantly provided. Advisedly we use the word " ear " 

 in place of " auditory organ." In all animals this organ 

 affords information of a double nature movement of the 

 external medium in which the animal lives, and movements 

 of the animal in the medium. When the animal moves, its 

 sensory hairs are displaced with regard to the otolith ; when 

 the water in which it is swimming pulsates, its otoliths are 

 shaken against the sensory hairs. Displacements of the 

 animal and agitations of the water produce similar effects. The 

 ear in this stage is an organ of touch. It might well be ques- 

 tioned whether an animal fitted with a piece of sensory appar- 

 atus of this kind is endowed with a sense which we may 

 properly, after reflecting upon our own sensations, term 

 " hearing." It is, however, stated that certain transparent 

 crustaceans, in which the functioning of the ear-organs may 

 be watched through a lens, show in these organs hairs of 

 varying length which vibrate to tones of different frequency. 

 This observation apart, it might be doubted whether fishes 

 hear, if we mean by the word " hearing " the recognition and 



